1. Field of the Invention
The present invention relates to a hologram recording apparatus for recording data in a hologram recording medium, a hologram recording method and a hologram recording medium.
2. Description of the Related Art
Hologram recording apparatuses for recording data in hologram recording media have been developed.
A hologram recording apparatus is adapted to superimpose signal light modulated by a spatial light modulator on unmodulated reference light on a hologram recording medium to record an obtained interference pattern.
There are two types of spatial light modulators, namely, an intensity type and a phase modulation type. The intensity type spatial light modulator controls the quantity of transmitted or reflected light to perform modulation, and permits use of, for example, a liquid crystal display device.
The phase modulation type spatial light modulator partly changes a light phase to cause interference so as to generate the distribution of light intensity, and permits use of, for example, a grating light valve (GLV) made by Silicon Light Machine. In the phase modulation type, digital data can be recorded in a hologram recording medium by, for example, associating a status wherein only zero-order diffracted light is produced from the spatial light modulator with “1”, while a status wherein only ±1-order diffracted light rather than the zero-order diffracted light is produced with “0,” respectively.
A GLV technology has been disclosed by Patent Document 1, namely, the gazette of U.S. Pat. No. 5,311,360.
Our research results, however, have revealed that a phase modulation type spatial light modulator produce diversified types of diffracted light rather than only the zero-order diffracted light and the ±1-order diffracted light. Such diversified diffracted light turns into noises when recording data in a hologram recording medium, leading to a possibility of errors in decoding the data.